I. Field of the Invention
This invention relates generally to high speed packaging machinery and more particularly to an improvement to a microprocessor controlled horizontal wrapper where product-out-of-registration conditions can be sensed and automatically cleared without damage to the cut/seal heads and without manual intervention.
II. Discussion of the Prior Art
In the Eaves et al U.S. Pat. No. 4,574,566 there is described a microprocessor-based control system for a horizontal wrapping machine. As has been pointed out in the "Background of the Invention" section of that patent, in a horizontal wrapping machine, a continuous film of packaging material is supplied from a roll and drawn past a film former which shapes the film into a continuous tube of packaging material. Products to be wrapped are supplied from a flighted infeed conveyor through the former and into the tube of packaging material such that the products are appropriately spaced from one another within the tube as the tube is drawn through heated finwheels. The finwheels not only act to draw the film from its supply reel and over the former, but also simultaneously creates a continuous longitudinal seal between the opposed side edges of the film tube. A transversely extending rotatably mounted blade and anvil at a cutting and sealing station cooperate with one another and with the tube of packaging material passing between them to create a transverse seal between adjacent entubed products while also severing the tube into discrete packages. Finally, the packaged products are deposited on a discharge conveyor leading to a cartoning station or the like.
As is further explained in the Eaves et al U.S. Pat. No. 4,574,566, the disclosure of which is hereby incorporated by reference, the drive motors for the infeed conveyor, the finwheels, the cut/seal head and the discharge conveyor are electronically controlled by separate, closed-loop controllers which receive commands from a programmed microprocessor. The advantages of that system over then-existing prior art horizontal wrappers, where synchronism was maintained using drive shafts, clutches, brakes and similar mechanical linkages, is fully set out in the aforereferenced Eaves et al patent and need not be repeated here. Suffice it to say that the microprocessor-based architecture of the horizontal packaging machine affords significantly greater flexibility in the overall setup, initialization, running, and change-over upon different product selection than could be achieved using earlier, prior art systems.
One problem not addressed in the Eaves et al patent is the situation which occurs when a product falls out of registration with the supposedly synchronized operation of the cut/seal heads. In one recent application of the Servotronic.TM. wrapping machine, which is the equipment manufactured and sold by Doboy Packaging Machinery, Inc., applicant's assignee, and made in accordance with the Eaves et al U.S. Pat. No. 4,574,466, it was desired to wrap synthetic sponges in plastic film. The sponges, however, had a somewhat curved configuration and, on occasion, the lugs or pusher fingers on the flighted infeed conveyor would slide beneath the trailing end of the sponge. That is to say, the sponges would occasionally ride up on the pusher lugs and, thus, would no longer be in precise registration with respect to the rotation of the blade and anvil of the cut/seal head. This would lead to the blade and anvil coming together with the product sandwiched between and was a serious cause of premature failure of the cut/seal heads. Furthermore, such an event would require the shut down of the packaging machine while the fault condition was cleared. This necessarily detracted from the production rate for the machine.
The present invention provides a solution to that problem. More particularly, an additional photoelectric sensor in the form of a radiation transmitter disposed on one side of the film tube and a radiation sensor positioned in alignment with the transmitter, but on the opposite side of the film tube at a location near the finwheel assembly, which is a precisely measured distance upstream of the cut/seal head station is employed to look for the presence of a product in a "window" at timed instants. If proper registration exists, no product will be detected. However, if the sensor detects a product intercepting the beam at the sampling time, an out-of-registration condition exists and the sensor triggers the execution of a software routine which is capable of preventing the out-of-registration product from coming between the blade and anvil of the cut/seal head. Upon detecting an improperly positioned product, the software causes the wrapper to come to a synchronized stop with the anvil and blade in its opened orientation and to automatically clear all products contained within the film tube downstream of the former. Once the film tube is so cleared, the high speed wrapper is again be made to function in its normal running mode.